Photographic contact-printing apparatus



Julie 1954 L. E. VAN DER GRINTEN 2.681,603

PHOTQGRPHIC CONTACT-PRIN'IING PPARATUS 3 Sheets-Sheet 1 Filed July 19, 1950 lOa. 46

INVENTOR LODEWIJK EVERT VAN DER GRNTEN QQWM2IKQM/ AT RN .VS

June 1954 L. E. VAN DER GRINTEN 2,681,603

PHOTOGRAPHIC conncm=mmmc APPARATUS Fi1ed July 19, 1950 5 Sheets-Sheet 2 FIG.6.

NVENTO R LODEWIJJK EVERT VAN DERGR\NTEN BY: 9

AT ORN EYS 1954 1.. E. VAN DER GRINTEN 2.681,603

PHOTOGRAPHIC conncmmmrmc: APPARATUS F1ed July 19, 1950 3 Sheets-Sheet 3 FIG9.

FIG.IO.

NVENTOR LODEWIJK EVERT wm ER GR\NTEN AT RNYS Patented June 22, 1954 PHO'IOGRAPHIC CONTACT -PRIN TIN G APPARATUS Lodewijk Evert van der Grinten, Venlo, Netherlands, assignor, by mesne assignments, to Chemische Fabriek L. van der Grinten N. V., Venlo, Netherlands, a corporation of the Netherlands Application July 19, 1950, Serial No. 174,665

Claims priority, applieation Netherlands July 21, 1949 19 Claims. 1

The nventon relates to a type of photographic contact-prnting apparatus comprising a panel of translucent materal curved in one direction, thus having straight generating lines on its surface, oo-operating on its convex side (which may be termed a straight convex surface) With a flexible applying apron for applying and pressing the material to be exposed onto the panel under tenson, and members engaging the feeding apron in a direction transverse to the generating lines of the panel in order to held the apron under tension. Exposure apparatus of this type, as thus far descrbed, is known.

Wth none of the known apparatus, provided with a curved panel and a lexble applying apron, is it possible to copy from books in the sense that a page from a book can be plaoed eetween the panel and the apron in the printing position without the said page first being removed, i. e. torn, from the boek. In none of the known apparatus is there suflicient spaoe er opportunity f01 accommodating the rest of the book during the printing of said single page from it and even if with the greatest difiiculty, accoh modation can be provided for the rest of the book, this involves a considerable deformatien of the book, which is undesirable. Moreover t is even then not possible to copy the page far into the fold of the book, so that with the known apparatus only thin periodicals can be dealt with,

and these only when they are prnted with a wide margin.

The present invention is concerned wth an improved form of apparatus which overcomes these difflculties. According to the present incomprises a lnearly curved exposure panel of light-transmittng material, adapted to be illuminated from the concave side thereof, an apron adapted to be laid close to the convex side of said panel and to sandwich between tself and the panel a sheet of lght-sensitve material and an orgnal sheet to be copied, the said apron terminatin in a thin flat edge along a line parallel to the generating lnes of the panel, means for moving the apron and panel relatively from a rest position in which they are apart to a working pestion in which the apron lies close to the panel, and vice versa, suoh that in the sad working position the said terminal edge lies against the panel, and means holding the said apren under tenson in a direction perpendicular to the generating lines of the panel said tenson means consisting of members pulling the sad terminal edge in the direction of the extension of the apron beyond said edge or members seeured 2 to the face of the apron more remote from the anel and pushing the said edge in the saicl direc- The invention will now be desoribed wth refer enee to the aocompanyng diagrammatic drawi1gs Whch illustrate simple apparatus and also apparatus including preferred eatures of the i11- vention.

Figs. 1 and 2 illustrate an apparatus for copying pages from books in the resting and the working postions respectvely.

3 and 4 smilarly illustrate an alternative apparatus or the same purpose.

Fig. 5 illustrates a form of apparatus embeying a flexible apron.

Fig. 6 illustrates a modified orm of the apparatus accordng t0 Figs. 1 and 2.

Figs. '7 and 8 llustrate a fu1ther alternative apparatus, again in the resting and the working positons respeotively.

Figs. 9 and 19 illustrate in the resting and werking positiens respeetively, apparatus embodying, a movng panel.

Referring to Fig. 1 a tube-shaped lamp I is looatecl wthin a curved panel 2. (in this oase a full-circle oylinder, mounted S0 as te be rotatable about its axis by means of members not illustrated). An applying apron 3 ends on the left in a flat anc thin terminal edge Ths terminal edge 4 is stiffenecl by means of a flat, straight steel rib extending 011 either sicle beyond the apron and to these extensions are securecl tape 5. The ether end of the apron lies against the oylinder 2 at the postion 6 and this end also has an extension te which two tapes l, provention photographic contact-printing apparatus vided en ether side of the apron ancl forming a oontinuation of the apron, are attached, these tapes l being looped about the oylnder and passing underneath the cylinder to the right. The tapes 5 are laid over two pulleys 8 and the tapes over tw0 pulleys 9. Below the apparatus these tapes are interconnected by means of two sprngs !ll (for the loop construc-tion ebtaned reference may be made to oopendng appleatien S81. 761,314.

The apron 3 with its edge 4 can be movecl te the right and back again; when 1lS dene, the apron Will Wind and unwind itself about e-5rl nder 2. Thus, the loop construotion wi-th the spring HJ described above Will keep the apron parallel to the axs of the eylincler 2 in every postion.

In Figs. 1 and 2 a book has been illustra-ted (in Fig. 1 in the restng positien and. in Fig. 2 in the werking postion), the page to be eepetl eeng designated by H; whle the photosensitive material on Which a reflex copy of the said page is to be producecl is designated by l2. The book is supported by a slide l3 mountecl ilexiloly on wheels H which are capable of running backwards and forwards on rails l5. When the slide I3 is moved to the rght on the rails 15, the apparatus reaches the position illustrated in Fig. 2. The page of the book to be copiecl and the superposecl photo-sensitive material are carried along between the cylinder 2 and feecling apron 3, and pressecl closely together as necessary for contactprinting. After the exposure the apparatus is returneol to the resting position of Fig. 1; the light sensitive material on which the reflex copy of the page 1! has been reprcluced. is removed, a resh page is put in readiness on the eeding apron 3 over the terminal edge l, resh lightsensitive material is laid over the page and the apparatus is again moved into the working position shown in Fig. 2. These operations may be repeated or successive pages and. the apparatus thus provides a simple method for copying pages trom books without the book itself having to be subjected to inconvenient pressure or other orces. As a result the books are not seriously deformed or damaged.

With sorne books it is clifrlclt to reach the olcl or spin even using an apparatus to Figs. 1 ancl 2; and a preferrecl form of the invention oy means of whioh the fold aan reachecl more efectively is obtainecl by arranging that the position of the apron on the curvecl panel is that in the worlring position the terminal eclge of the apron eoineicles with a free edge of the panel on one of its generating lines, i. e. so that the saici terminal edge of the apron regis ters with the free eclge of the panel as accu.- rately as possible. A simple erneodiment of such apparatns is illustrat-ecl in Figs. 3 and i, Which again show the resting and the working positions respeo-tively.

Reerring to Figs. 3 and the apparatus conprises a eurved panel 2a, apron 5a having a terminal eclge (ia, a holeler or ledge i3a for the book, a support 5 for the back of the loook. The drawings show the page H te be oopiecl and the photosensitive material 22. The 2a has a fixecl position in the apparatus tli1 is fixed relative to the i, located about as indieatezi in Fig. 3, arouncl which the helder i3a is rnoved into the werking position, illnstrated in 4, With the aid of the handle S4. Then the free edge 58 of the panel will coincide accurately with th edge of the apron 3a, while the part of the book projeeting to the left 1emains free, as illustraterl. this way the eclges 18 and 6a aan enter far into the folcl of the book, so that it becomes possible to copy the parts printed near this fold. The apron 2a anrl its terminal etlge 4a are kept parallel to the panel in essentially the same manner as with the apparatns according to Figs. 1 and 2, by means of the two springs Ia engaging tie terminal edge ila on either side of the apron near saicl terminal eclge. At the other encl the apron is astened at il. The stiiening of the terminal edge may project, just as in the apparatns aecording to l ancl 2, on either sicle of the free terminal edge, and these projections may be freely supporteol the hoicler i3a. In Flgs. 3 ancl 4 these supports have been omitted ior the salie of elearness. When the apparatus is in the workng position, a souree of light may be providecl 01 the apparatus may be movecl towards a source of iight or be exposed, for example, to sunlight.

Fig. 5 illustrates diagrammatically that a curved exposure panel 21) aan move up and. down in the direction of the arrows I ancl 22. The apron 317 is lexible in this case (made, ior example, of rubber) and astene-cl at 2! over its ful1 Wdth. When the panel 2b moves in the direction of arrow 22, the free edge f of the panel will meet the terminal edge 4"0 of the apron as acourately as possible. Located in this terminal edge il) is the end of the supporting plate 22, which is fixed, in the apparatus. This supporting plate 22 thus acts as a pushing member on the terminal eolge 4?) and gives a fixeol position to this terminal edge 4b in the apparatus.

The construction with a pushing rnemoer in the form of a plate onding in the terminal edge of the apron has been founcl to be particularly eificient. A form of apparatus aocorcling to the invention using such a pushing plate is illustrated diagrammatically in Fig. 6. The apron 3e and the two sicle tapes lc form a loop about the 0311- inder 2e in the manner desoribecl in the U. S. applioation Ser. No. 761,314, in the same gen eral manner as in the apparatus of Figs. 1 and. 2. The tapes 'c are passecl downwards over the pulleys 24 running on shafts which are connected to the plate 220 by means of the snpports 2-3. The whole of the loop comprising the aprc-n 3c and the tapes ie is kept under tensien by the spring lllc, whieh is fastencl at 23 to the bottom 01 the plate 220. Just as in the apparatus of Figs. 1 ancl 2, the cylinder 2e is rotatable about the fixed shaft. When the plate 220 is moved to the right, the apron 3c winds itseli onto the eylincler 2c, ancl the apparatns thus reaclies the werking position, in Whieh Werking postion the terminal edge 4c will touch the lowest generating line of the cylinder. Gn tln's terminal eclge c a book with the page to be copied and the superposed light-sensitive material may plaoetl in exaetly the same way as with the apparatus de scribed above. Ihe psling piate 22e in this apparatus has the additional useful funetion of constituting 2, kind of table with the apron piaeed upon it, so that the said apron is supported, which acilitates placing and positioning the book while the apparatus is in the resting position. n Fig. 6 neither the means with which the plate 22e is l :ept parallel to itseli cluring the ll' /Gi9l, nor the supports required for earrying the pook, have been illustrated but these ineans niay ha" e the sarne construction as those of Figs. l 2.

Apparatus employing a panel in the form of a cylinrler, as illustratei in Figs. l, 2 an;l 6, presents the advantage of high efrloieney tiuring e:; posure, ifas is techi1ically possible-a tube lamp is usecl as the sonree of light i. On the other hand, as will be apparent rero 3, 4 and 5, the registration 0 an edge of the panel with the terminal edge of the apron presents important advantages wnen Copying pages irom books. In Figs. 7 and 8 (whieh illustrate the resting and werking posiyions respeetively) an apparatus is illustrated diagramnatical'ig witn whioh both 'aclvantages are obtaine-el.

Referring te Figs. 7 ELII( 8 the oylinoer M is interrupted, as illustrated, by a slot whieh is fillecl up bya recesse'cl cap 27, the oylinoler thus having an edge extencling on a generating line. In this apparatus the apron 3d, as illustrated, is not extended with the aicl of tapes looped a'nout the cylinder, as in the apparatus of Figs. 1, 2 and 6, but it is passed outside the cylinder over the pulleys 26, the pulley 22d, the spring Hld,

and the support 23d, in the manner of Fig. 6. Its ether end terminates in the flat edge 4d.

In the resting position of Fig. 7 a boek with a page 1! and lght-sensitive material l2 may be intreduceci as diagrammatically illustrated anri as indioated in Figs. 1 and 2.

Fig. 8 illustrates the werking position, which is reached by shifting to the right the plate 22ci with the terminal edge 4d, of the apron 3d, while the regstration of the edge l8d of the cylnder with the terminal edge 4d of the apron makes it possible te reach the feld of the book, as llustrated.

Figs. 9 and 10 illustrate an apparatus in whcn, in passing from the resting position (Fig. 9) te the werking position (Fig. 10), nether the terminal eclge 4e nor the book placed in the apparatus meed be displaced. The book may, of oourse, be supported as above, fer example, with a support 16 as in Figs. 3 and 4.

Referring te Figs. 9 and 10, the apparatus includes a table 28 and an exposure casing '29 with reflector. ''he apron is fastened to the panel er te the strueture supporting the saicl panel at 39. TWO flexiele tensien members 3! provcled on either sicle ei 'the apron are fastenecl at 35 te the panel or easing, pass along the outside of the cnrved panel or the corresponding part of the expesure easing towards the back of the plate 22e, where they pass over pulleys 24e, in the manner of Fig. 6, ancl are tightened by means of the springs e flxed te 23e. These flexble tension members 3! thus cross t-he apren and run onto and off the curved panel in th reverse direction te tne apron itself. This device keeps the leerling apron 3d ander constant tension, on the one hand via tl1e plate 22e and on the other hand via the panel system. A hanclle 32 for the expesure oasing is provi.e and the plate 226 is supportecl by the supporte 33 and connected te the table 28. I'he supperts leave the bottem surface of the plate 22e substantlally free. The plate 22e engages the thin fiat terminal edge 4e of the apren 3e. 'Ihus, the tensien member acting on the terminal edge again censtitute a plate-shapecl pushing member, although tne tensien is ultimately produced by the spring l!e. In moving from the resting positon te tl1e werking pesition, the exposure casing 29 is transferred by means of the handle 32 from the positen of Fig. 9 te the position of Fg. 10 ancl kept in the latter pesition, and all the concltions required 'er the contact-printing ar then fulfilled 7hat I claim is:

1. In a contact photoprinting apparatus, a curved lght-pervious expesure panel havng an outer surfaee convex in ene direction ancl straight in the transverse direction, a flexible apron held te said surfaee, tlxe panel and apron being relatively mevable between a leading pesitien in whch a pertion of the apren extends away frem said surface in a plane tangential therete te receive sheet materal laid over such portien and an exposing pesition in which sueh perton holds the material wrappecl against said surface, a thin flat 21-I1d sc terminal edge on an end of apron porten and means censtantly holding said edge substantially parallel te generating lines en said surface and in said tangential plane, and means continueusly holding the apron stretched between said terminal edge ancl he panel so that the apren extends tangentally rem saici surface te said eclge in a fiat plane in the loading position of the panel and apron, said terminal edge being held free of ebstructions in said loading p0sition so that it enters readly into the -elcl of en open book placed thereaganst, sad. surface terminating at a free eclge of the panel on one of its generating lines, said re panel eclge substantially ceineiding with said terminal e ige in said exposing postien anc beng bordered. ley unebstructed space accemmeclatng a bulge of the open boek.

2. An apparatus as described in claim 1, sacl panel being in the form of a eylincler having a recessecl cireurnferential area orming said unobstrueted space.

3. In eontaet photeprintng apparatus, a eurvecl lght-pervous exposure panel having an outer suriaee eonvex in one directien and straight in the transverse clrectien, a flexible apron held te saicl surfaoe and movable relative te t in transverse te its generating lines between a leaclng pesitien in which a portion of the apren extends straight rem said surface te reeeive sheet material laid thereover and an exg pesition in which saici perton holols tne eratng lines, means eontinuously holding the apron stretched between said terminal edge the panel holding said terminal e lge uneL strueteel in loading positon so that eclge enters readily into the feld of an epen beek plaeel thereagainst, and a movable carrier underlying sacl edge te support sueh book, the carrier b movable aleng saicl path with sai-el terminal er An apparatus e.s described in claim 3, the path of saicl apron portion bei'ng bstantially tangent te saicl surace, and a traclaway substantially parallel te saici path fer supperting sad carrier.

5. In a contact phetoprintng apparatus, a cylindrically curved light-pervious exposure panel meuntee or retaten aeeut its axis, a fie:nele apren held te the convex surfaee of the panel and rnovable with panel rotation in a path tramverse te said axis between a loacling positien in which a portion of the apron extends tangentally from said surfaee te receive sheet material te be expesecl and an exposing postien in whieh suel1 pertien holds the materal wrapped against said surfaee, and a reeipreeable werk suppert presenting a substantially flat workin= surace movable below the panel in a path substantially tangent te the panel surface, said apren portion terminating at the orward end of said werking surlace ancl forming therewith a thin stif terminal edge parallel te sairi axis for inserizien nto the fold. of an open book placed thereaganst.

6. In a centaot photoprinting apparatus, a c lindrically curved light-pervious expesure panel mounted for retation about its axs, a fiexiele apren held te the cenvex surface of the panel and movable with panel retatien in a path tra. verse te sad axis het-ween a leading pesten in whieh a pertien of the apron extends tangentially frem said. surface to receive sheet al te be exposed and an exposing pesiten in wl1i-ch such portien helds the material wrapped against saici surface, and a reciprocable werk support presenting a substantially fiat werking surface movable below the panel in a path substantially tangent te the panel surface, said apron per ion terminating at the forwarcl end of saicl werking surface anti formng therewith a thin sti terminal edge parallel te sad axis ler insertion into the old of an open book placed thereagainst, ancl tensioning means interconnecting the panel and 7 a backvvard part of said support so as to held the apron in a stretched condition.

7. An apparatus as describecl in claim 6, said tensioning rneans inclurling spaced elongated flexiole mernloers disposecl on either side of the apron and extending rom the panel surface to a backward part of said werk support.

8. An apparatus as clescrbed in claim 6, said tensioning means including spaced elongated flexible mernbers dsposecl on either side of the apron and extending from the panel surfaee to a backward part of said work support, the apron and said fiexible members having interconneeted end. portions to form a contnuous band, the band being looped about the panel vvith the apron and said rnembers crossing eaoh other at and extending in opposite directions from the point of tangeney of said working surface.

9. An apparatus as described in claim 6, said work support comprising a book holcler spaced helow said terminal edge.

19. In a contact photoprnting apparatus comprising a curveol light-pervioug panel having an outer surface convex in one direction and straight in the transverse direction, a light source at the concave sicle of said panel and a flexible apron fer applyng sheet materlal to said surface for exposure through said panel, the panel and apron being relatively movable between a loading position in which a portion O the apron enoling in a transveree terminal eclge extencls away ro1n said surface in a plane tangential thereto to receive such material laicl over such portion and an exposing position in whieh such portion is wrapper aganst said surfaee to holcl sueh inaterial thereagainst, stifiening means rendering said terminal edg'e substantially flat, thin and rigid, n1eans supporting the stiffeneci terminal eel-ge in said tangential plane in a position ree rom obstructions and substantially parallel to the generating 111185 of said surface, so that said eclge aan enter readily nto the old. of an open boel; placed thereagainst when the panel and apron are in loacling position, and means continuonsly applying longitudinal tension to the apre-n up to said stifienecl terminal erge so that said apron poition is stretehed fiat up to said edge in said loaclng position and sandwiches sheet material laid over such portion tightly against said surface as the panel and apron are relatively movecl to exposing position.

11. In a contact photoprinting apparatus comprising a ourved lght-pervous panel having an Outer surface convex in one direction and straight in the transverse direction, a light source at the coneave sicle of said panel and a flexible apron for applying sheet material to said. surace or exposure through said panel, the panel and apron 'neing relatively movable between a loa ing position in which a portion of the apron encling in a transverse terminal edge extends away from said surface in a plane tangential thereto to receive such material laid over suoh portion and an exposing position in which such portion is wrappecl against said surface to holcl such material thereagainst, stiiening means renclering said terminal edge substantially flat, thin and rigicl, means supporting the stiffened terminal eoge in said tangential plane in a position ree rorn ohstruetions and substantially parallel to the generating lines of said surfaee, So that said edge can enter reaolily into the folcl of an open boek plaeecl thereagainst when the panel and apron are in loading position, and means continuously applying longitudinaltensionto the apron up to said stiffened terminal edge so that said apron portion is stretchecl lat up to said edge in said loacling position and. sandwiches sheet material laid over such portion tightly against said surface as the panel and. apron are relatively movecl to exposing position, said panel presenting a free edge substantially parallel to said generating lines and substantially coincicling with said terminal eclge in said exposing position.

l2. An apparatus as described in claim 10, said supporting means holding said stiiened terminal eolge in a relatively f1xecl position and said panel and. said supporting means being relatively movable bodily to establish said loading and. exposing positions.

13. An apparatus as described in claim 10, said supporting means holding said stiiened terminal edge in a relatively fixecl position and said panel and said supporting means being relatively movable bodily to establish said loacling and exposing positions, said panel presenting a free eclge substantially parallel to said generating lines and substantially coinciding with said terminal edge said. exposing position.

14. In a contact photoprinting apparatus oomprising a curveol light-pervous panel having an enter surace convexin one direction and straight in the transverse direetion, a light source at the ooncave side of said panel and a fiexible apron or applying sheet niaterial to said surface or exposure throu h panel, the panel and apron being relatively n1evable between a loading position in which a portion of the apron enoling in a transverse terminal edge extenols away from said surface in a plane tangential thereto to reeeive such material laid over such portion and. an exposing position in which such porticn is wrappeol against said surace to hold. such material thereagainst, stfiening means rendering said terminal enge substantially flat, thn and rigid, means supporting the stiened terminal edge in said tangential plane in a position ree rorn obstructions and substantially parallel to the generating lines of said surfaee, so that said eclge aan enter readily into the olcl of an open boek plaeed thereagainst when the panel and apron are in loaclingpostion, and rneans continu ously applying longitudinal tension to the apron up to said stiffenecl terminal erlge so that said apron portion is stretched flat up to said edge in said loading position and sandwiches sheet Inaterial laicl over such portion tightly against said surfaee as the panel and apron are relatively movecl te exposing position, there being a rigid. plate nnclerlying said panel and said. apron and presenting across its forward end a thin rigid eclge engaging said terminal edge of the apron so as to constitute said supporting means and said stiffening means.

15. In a contact photoprinting apparatus comprising a curved lght-pervous panel having an outer surface eonvex in one direction and straight in the transverse direction, a light source at the conoave side of said panel and a lexible apron for applying sheet material to said surface for exposure through said panel, the panel and a.pr0ll being relatively movable between a loading position in which a portion of the apron encling in a transverse terminal edge lies away from said surface to receive such material lad thereover and. an exposing position in which such portion is wrapped against said surface to holdsuch material thereagainst, stifiening means rendering said. terminal edge substantially flat, thin and rigid and means supporting the stiiened terminal edge in a position free from obstruct-ions anel substantially parallel to the generating lnes of said surface, so that said edge can enter rea-ily into the folcl of an open book placecl thereagainst when the panel and apron are in lcacling position and means continuously applying longitudinal tension to the apron up to saicl stififened terminal edge so that said apron portion is stretched. in a flat plane up to said eclge in said loading position and sandwiches sheet materal laid over sucn portion tightly against saicl surface as the panel ancl apron are relatively moved to exposing there being a rigid plate underlying said panel 8.Il said apron and presenting across its fc1wvarcl end a thin rigid edge engaging said. terminal edge of the a ron so as to constitute saicl supporting means ancl said stilening means, sai:l applying means comprising fie:aible 1nernbe stretchecl between said panel and a baek. part of said plate.

15. In a contact photoprinting apparatus corn prising a curved light-pervious panel having an outer surf-ace convex in one direction anti straight in the transverse direction, a light souree at he concave side of said panel and a flexib'ze a ion for applying sheet material te saiel snrace cr exposure thrcugh said panel, the panel 2Yld apron being relatvely movable between a loading p sition in which a portion of the apron encling: in a transverse terminal edge extencls away from surface in a plane tangential thereto to receive such material laid over such portion an e:; posing position in which such portion is \1 :appecl against saicl surface to holcl su.ch mater -l tliere against, a rigd plate underlying said anel ancl said apron and having across its forward end. thin rigid edge engaging said terminal edge of the apron, saicl thin rigid edge rendering saicl terminal edge substantially flat, thin ancl ii-gii and holding it in saicl tangential plane in a relatively fixed position substantally parallel to the generating lnes of said surface, means supporting said plate so that t holds saicl terminal eclge tree from obstructions when the panel anti apron are in said loading position, and means extending from a backward part of said plate for continuously applying longitudinal tension to the apron up to said terminal edge so that sair l apron porton is stretchecl flat up to said edge in said. loacl ing position and sandwiches sheet material laicl over such portion tightly against saicl surface as the panel and apron are relatively moved to exposing position.

17 In a contact photoprinting apparatus comprising a curved light-pervious panel having an outer surface convex in one directon and straight in the transverse direction, a light source at the concave sicle of sad panel and. a flexible apron for applying sheet materal t said surface I'or exposure through said panel, the panel and apron being relatively movable between a loading position in which a portion of the apron encling in a transverse terminal edge extends away from said surfaee in a plane tangential thereto to receive such material laicl over such portion and an exposng poston in whch such portion is wrapped. aganst said surface to hold such material thereagainst, a rigid plate underlying said panel and sad apron and having across ts orward end a thin rigid edge engaging; saicl terminal edge of the apron, saicl thin rgid edge rendering saicl terminal eclge substantially flat, thin and rigirl and holding it in saicl tangential plane in a rela tively fixecl postion snbstantially parallel to the generating l nes of surface, means snppcrting saicl plate so that it holcls sacl terminal edge ree from obstructions when the panel and apron are in said loadng position, ancl means eztending from a backward. part of saicl plate or continuously applying longitudinal tension to the apron up te saicl terminal enige so that said apron por tion is stretched flat up to saici eclge in load ing position and sandwiches sheet 1naterial raid over snch portion tightly against said surfaee as the panel ancl apron are relatively inovecl to exposing position, sai l panel presenting a free edge substantially parallel to said. generating lines ancl substantially coincicling With saicl ter inal eclge in sai-zl exposin position.

18. In a contact photoprinting apparatus, a curvecl light-pervous panel having a convex outer surface which is straight in transverse direction ancl extends in an are of less than 360 between opposite end edges of the panel, a light souree at the concave side of saicl panel, a flexible apron held to said panel ancl arrangecl tc extencl irorn one of saicl encl edges over saial surace to a transverse terminal edge of the apron, said panel lld saicl apron being relatively mot-a'ole between a loading position in which the apron extends tangentially away from saicl surface to receive sheet material laid thereon for exposure E.l1d an exposing position in which the apron is wrapped against said surface te holcl sueh material thereagainst, a rigcl plate underlying said. panel ancl saicl apron and having acrosg. its forwarcl end a thin rigid edge engaging said terminal eclge of the apron, saicl thin ri id eclge rencle1ing saicl terminal eclge substantlally flat, thin anti rigid and holding it in a relatively fixecl position snbstantially parallel to the ge. erating lines of said surface, the other of said end edges of the panel substantially -oincidng with said. terminal edge in said exposing position, ancl means extending to saicl surface irom a baclzwarcl part of said plate for continuously applying tension to the apron so as to keep t stretched longitudinally up to said terminal edge.

19. An apparatus as descrbed in claim 18, sad tension applying means including spaeed elongatecl fiexible members disposed. on either side of the apron and crossing the apron approxirnately at its point of tangency to said suriace.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 704232 Bell July 8, 1962 720,862 Wagenhorst Feb. 17, 1903 2,512,487 De Lacy June 29, 2585519 Grinten Feb. 12, 1952 FOREIGN PATENTS Number Country Date 231,309 Germany Aug. 12 1909 62,224 Netherlands Dec. 15, 1948 949,583 France Feb. 21, 1949 

